Effect of High Temperature on the Aqueous H2S Corrosion of Mild Steel

The understanding of sour corrosion mechanisms is an important but still largely elusive target, especially as it pertains to the interaction between corrosion and corrosion product layer formation. The objective of this work was to investigate the effect of high temperature on the corrosion kinetics of carbon steel and the formation of corrosion product layers in sour environments. H2S corrosion experiments were performed at 80 degrees C, 120 degrees C, 160 degrees C, and 200 degrees C with 4 d exposure. Linear polarization resistance was used to determine the corrosion rates. The corrosion products were identified by x-ray diffraction and examined by scanning electron microscopy together with energy dispersive spectroscopy. The results indicate that with the increase of temperature, the initial corrosion rates increased, then reached a steady state over time. Two distinct layers were found in the corrosion products. An inner iron oxide (postulated to be Fe3O4) layer was unexpectedly observed at every studied temperature, while the outer layer was identified as mackinawite, troilite, pyrrhotite, and pyrite at 80 degrees C, 120 degrees C, 160 degrees C, and 200 degrees C, respectively.